1. Field of the Invention
This invention relates to a semiconductor dynamic quantity sensor having a movable electrode and a fixed electrode for detecting a dynamic quantity applied thereto based on a change in interval between the movable electrode and the fixed electrode.
2. Description of the Related Art
This kind of semiconductor dynamic quantity sensor is disclosed in, for example, JP-A-11-326365. FIGS. 1A and 1B show a constitution of this kind of semiconductor dynamic quantity sensor.
The sensor is, as shown in FIG. 1B, formed by performing a micro-machining technique to a semiconductor substrate composed of a first semiconductor layer 201, a second semiconductor layer 202, and an insulation layer 203 interposed between the semiconductor layers 201, 202. For example, the semiconductor layers 201, 202 are made of silicon (Si), and the insulation layer 203 is a Si oxide film.
A beam structure, which is composed of a movable electrode 204 and fixed electrodes 205 opposed to the movable electrode 204 with detection intervals 206 defined therebetween, is defined by grooves in the second semiconductor layer 202 of the semiconductor substrate. In the figures, each of the electrodes 204, 205 has a comb-shape. The movable electrode 204 has a weight portion 207 and several pole portions 208 projecting from the weight portion 207, and the fixed electrodes 205 have several pole portions 209, each of which faces aside face of a corresponding pole portion 208.
The first semiconductor layer 201 and the insulation layer 203 constitute a support substrate, and an opening portion 210 open at a side of the second semiconductor layer 202 is formed in the support substrate. In this example, the opening portion 210 is a rectangle and passes through both the first semiconductor layer 201 and the insulation layer 203 in the thickness direction thereof.
A pair of opposed sides forming the opening portion 210 fixedly support both ends of the weight portion 207 with elasticity. The movable electrode 204 can displace above the opening portion 210 in a direction indicated by arrow X in FIG. 1A upon receiving a dynamic quantity (such as acceleration). Supporting portions 211 of the fixed electrodes 205 are fixedly supported by another pair of opposed sides forming the opening portion 210, different from those supporting the weight portion 207.
In the semiconductor dynamic quantity sensor described above, when the movable electrode 204 is displaced in response to the dynamic quantity applied thereto, the dynamic quantity is detected based on changes of the detection intervals 206.